Liquid crystalline compounds and compositions

ABSTRACT

Liquid crystalline materials comprised of substituted phenyl pbenzoyloxybenzoates are useful in electro-optical elements. These materials have low crystal to mesophase transition temperatures and have a broad mesophase temperature range.

on amsmaa United States Patent 1 VanMeter et a1.

[ LIQUID CRYSTALLINE COMPOUNDS AND COMPOSITIONS [75} Inventors: James P.VanMeter; Bruce H.

Klanderman, both of Rochester, N.Y.

[73] Assignee: Eastman Kodak Company,

Rochester, NY.

[22] Filed: Aug. 15, 1973 [21] App]. No.: 388,516

Related US. Application Data [63] Continuation-impart of Ser. No.247,563, April 26,

1972, abandoned.

[52] US. Cl. 252/299; 252/408 LC; 260/473 R; 350/160 LC [51] Int.C1...C09k 3/00; GOln 31/00; G0ln 33/00; G02f 1/28; G02f 1/36 OBSERVER I1I I [451 Oct. 28, 1975 3,826,757 7/1974 Wong 252/408 3,836,478 9/1974Green et al 252/408 FOREIGN PATENTS OR APPLICATIONS 2,139,628 2/1973Germany 252/408 2,024,269 12/1971 Germany 252/299 2,121,487 12/1971Germany 252/299 2,009,528 9/1971 Germany 252/299 OTHER PUBLICATIONSMolecular Structure and Liquid Crystalinity, Phenylene Bis(Alkoxybenzoates), Arora et al., J. Org. Chem., V01. 35, N0. 12, pp.40554058, (1970).

W. Kast, Landolt-Bomstein, Springer, Berlin, 6th Ed., (1960), Vol. 2,Part 2a, pp. 266, 295.

Primary Examiner-Leland A. Sebastian Assistant Examiner-T. S. GronAttorney, Agent, or FirmI-I. M, Chapin [57] ABSTRACT Liquid crystallinematerials comprised of substituted phenyl p-benzoyloxybenzoates areuseful in electrooptical elements. These materials have low crystal tomesophase transition temperatures and have a broad mesophase temperaturerange.

8 Claims, 1 Drawing Figure U.S. Patent Oct. 28, 1975 B M v VOLT/16ESOURCE Y OBSERVE/i FIELD OF THE INVENTION This invention relatesgenerally to liquid crystalline composition. More particularly, theinvention relates to novel nematic liquid crystalline materials andmixtures and the use thereof in elector-optical devices.

BACKGROUND OF INVENTION Nematic liquid crystalline compositons are usedin various electo-optical devices which involve the modulation of light,such as light valves and optical display devices. Such light valvestypically are controlled by an electric field and operate when theliquid crystalline material is in its mesomorphic state. Generally, whenno electric field is applied to a nematic liquid crystalline material, adevice containing a thin layer of this material is relativelytransparent to light. When an electric field is applied to the liquidcrystalline material above a threshold value, the device appears tobecome opaque in the region of the field. This opacity is believed to bedue to the scattering of light by domains of the liquid crystalmolecules which align themselves in the field. A dynamic scatteringeffect is seen when the aligned molecules are perturbed by ions "bumpinginto them and causing movement thereof.

The electro-optical effect due to alignment of domains of the nematicliquid crystal molecules in an electric field may be employed intransmissive, reflective, or absorptive-type flat-panel displays, inlight shutters, and in other applications.

Nematic liquid crystalline materials exhibit a characteristic threadtexture when properly viewed, and this texture is believed to be theboundaries of many domains or clusters in which the liquid crystallinemolecules have a fixed orientation. According to the cluster theory ofnematic liquid crystals, the clusters are randomly oriented, whichaccounts for the light scattering properties and for the turbidappearance of a fairly large volume. In addition, nematic liquidcrystalline molecules typically are electrically and magneticallyanisotropic. Thus, upon the application of an electric or magnetic fieldto a layer of randomly oriented nematic liquid cyrstals, the clusterstend to become oriented in a particular direction. This orientationresults in changes in the light-scattering and birefringent propertiesof the layer. The degree of orientation attained by the moleculesusually is dependent upon the magnitude of the applied field.Accordingly, the lightscattering properties and birefringent propertiesof a layer of nematic liquid crystalline material can be modulated withan electric or magnetic field.

Numerous examples of liquid crystalline materials have been described inthe literature. However, to date, there is little certainty involved inpredicting the exact properties of any hypothetical liquid crystallinecompound. In view of this lack of predictability, the search continuesfor suitable nematic liquid crystalline compounds. From the standpointof ease of handling, it is desirable to have materials which have lowcrystal to mesomorphic transition temperatures and preferably the liquidcrystalline materials should have a broad temperature range over whichthe nematic phase exists.

DESCRIPTION OF PRIOR ART Recently, Dewar and Goldberg reported in J.Org. Chem., 35, 271 l (1970) the preparation of liquid crystallinep-phenylene esters of para-substituted benzoic acids (Type A) andpara-substituted phenyl esters of terephthalic acids (Type B) as shownbelow.

i ii

Type A i ii Type B These materials have crystal to mesophase transitiontemperatures above 100C and mesomorphic ranges of 35 to S. L. Arora etal. described in J. Org. Chem., 35, 4055, (I970) liquid crystalline2-methyl-l ,4- phenylene esters of parasubstituted benzoic acids (TypeA). These materials have lower crystal to mesophase transitiontemperatures than the corresponding unsubstituted hydroquinonederivatives.

Excluding consideration of the methyl substituent in the Arora et alcompounds, the liquid crystalline compounds described in the referencesabove may be viewed as being derived from the symmetrical intermediateshydroquinone or terephthalic acid. In addition, the terminalsubstituents R and R are equivalent, thus adding to the symmetry of themolecule. Recently, S. A. Haut et al., described in Abstracts of Papers,[62nd ACS National Meeting, Washington, D. C., Sept. 12-17, 1971, thepreparation of a series of liquid crystalline compounds in the Type Aclass in which the two terminal substituents R and R were notequivalent. It was found that this increase in dissymmetry resulted inlower crystal to mesophase transition temperatures. W. Kast inLandolt-Bornstein, 6th ed., Springer, Berlin, 1960, Vol. II, Part 2a, p.266, reported the only known unsymmetrical derivatives which have theformula below (Type C).

This class of liquid crystals may be viewed as derivatives of theunsymmetrical molecule p-hydroxybenzoic acid. All reported examples havehigh crystal to mesophase transition temperatures and, with oneexception, rather short mesomorphic ranges.

SUMMARY OF THE INVENTION ex -o Type C BRIEF DESCRIPTION OF DRAWINGS Thefigure is a schematic sectional view of an electrooptical display deviceof the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The objects and advantages of thisinvention are provided by liquid crystalline materials which aresubstituted phenyl-p-benzoyloxybenzoates having the formula:

wherein:

one of the terminal substituents R and R represents (a) an alkyl grouphaving from 1 to about 18 carbon atoms and typically having 1 to about12 carbon atoms such as methyl, ethyl, isopropyl, isobutyl, octyl,decyl, dodecyl, pentadecyl, etc, and including the correspondingsubstituted alkyl groups having small, polar substituents containing nomore than 8 atoms (preferably no more than 5 atoms) such as methoxy,ethoxy, cyano, halogen and similar substituents or (b) a cyano group;and the other of R and R represents (a) an alkyl group as describedabove or (b) an alkoxy group having 1 to about 18 carbon atoms andtypically having 1 to about 12 carbon atoms such as methoxy, ethoxy,isobutoxy, hexoxy, dodecoxy, etc, and including the correspondingsubstituted alkoxy groups having small, polar substituents as describedabove for the alkyl group; and

at least one of the lateral substituents R, R, R R, R and R represents acyano group or a halogen atom (chlorine, fluorine, etc) and theremaining substituents represent relatively small moieties typicallycontaining no more than about 8 atoms and preferably no more than about4 atoms such as a methyl group, an ethyl group, a methoxy group, a cyanogroup or a halogen atom (e.g., Cl, F, etc), a nitro group; of course,all of the remaining substituents can also be hydrogen atoms.

Especially useful compounds are those of the formula 1 above wherein:

one of R and R represents (aan alkyl group including substituted alkylas described above having 1 to about 12 carbon atoms or (b) a cyanogroup; and the other of R and R represents (a) an alkyl group having 1to about 12 carbon atoms as described above or (b) an alkoxy groupincluding substituted alkoxy as described above having 1 to about 12carbon atoms in the alkyl moiety; and

at least one of R, R, R R, R and R represents (a) a cyano group in whichcase the remaining substituents are selected from a hydrogen atom, amethyl group, a halogen atom and a nitro group or (b) a halogen atom inwhich case the remaining substituents represent hydrogen.

Among the preferred compounds from the standpoint of physical propertiesare compounds of the formula:

o e o X wherein:

R is an alkyl group having about 4 to 8 carbon atoms (e.g., isobutyl,pentyl, hexyl, heptyl, octyl); R is (a) an alkyl group having about 4 to8 carbon atoms as described for R or (b) an alkoxy group having 4 to 8carbon atoms (e.g., isobutyloxy, pentyloxy, hexyloxy, heptyloxy,octyloxy); and X is a halogen atom, preferably chlorine.

Exemplary of various useful compounds described above are those given inTable l below along the their indicated transitional temperature ranges:

N refers to the nemalic range S refers to the smectic range Mixtures ofthe liquid crystalline materials of this invention are especially usefulin that compositions can be formed which have a very low crystal tomesomorphic transition temperature. Particularly useful are compositionscontaining about 35 to 65% by weight of one compound having Formula 11above together with about 65 to 35% by weight of a different compoundhaving Formula 11 above. Useful mixtures can also contain othersubstituted phenyl p-benzoyloxybenzoates having Formula I above. Inaddition, useful mixtures as described above can further contain simpleesters such as the various p,p'-substituted phenyl benzoates such asthose having the formula:

wherein one of R and R" is an alkyl or alkoxy group having 1 to about 12carbon atoms (preferably about 1 to 8 carbon atoms) and the other of Rand R" is also an alkyl or alkoxy group as just described or a cyanogroup. Mixtures containing such simple esters can be comprised of (a)about to 70% by weight of the simple ester with (b) about 95 to 30% byweight of at least one compound having Formula I as described above.Useful results are obtained with only up to about 10 to 30% by weight ofsuch simple esters with the remainder comprising a mixture of compoundshaving Formula 11 above.

A 1:1 mixture by weight of Compound No. 12 with Compound No. gives acomposition having a mesomorphic temperature range of 3 to 112C. Al:l:3:3 weight ratio mixture of p-pentylphenyl pmethoxybenzoate,p-pentylphenyl p-propylbenzoate, 4-pentylphenyl2-chloro-4-(4-pentylphenylbenzoyloxy)benzoate (Compound No. 20) and4-pentylphenyl 4-(4-pentyloxy-3-cyanobenzoyloxy)benzoate (Compound No.exhibits useful liquid crystalline properties and is a liquid at roomtemperature.

The compounds of this invention are typically prepared by reacting theappropriately substituted benzoyl chloride with a substituted pheylp-hydroxybenzoate in a suitable reaction medium such as pyridine. Thereaction can be conducted at most any convenient temperature andgenerally is conducted at room temperature. The desired substitutedphenyl p-hydroxybenzoate can be prepared by the technique of W. W.Lowrance, Jr., Tetrahedron Letters, 3453 (1971). Representativepreparatory techniques are described further in the following examples.

EXAMPLE 1 Preparation of 4-pentylphenyl 2-chloro-4-hydroxybenzoate To asuspension of p-pentylphenol (0.15 mole) and 2-chloro-4-hydroxybenzoicacid (0.10 mole) in toluene (500 ml.) is added concentrated sulfuricacid (0.5 g.) and boric acid (0.31 g.) (5 mole percent). The reactionmixture is refluxed for 29 hours under a Dean-Stark trap. The solvent isthen removed under reduced pressure and the product is washed withligroin. The resulting 4-pentylphenyl 2-chloro-4-hydroxybenzoate isrecrystallized from an ethanol/water mixture to give 25.6 g., 81% ofpure product, m.p. l4915lC.

EXAMPLE 2 4-n-pentylphenyl 2-chloro-4-( 4-pentylbenzoyloxy )-benzoate Amixture of 4-pentylphenyl 2-chloro-4- hydroxybenzoate (.0075 mole)prepared as in Example 1 and p-pentylbenzoyl chloride (.0075 mole) inpyridine (35 ml.) is stirred at room temperature for 5 hours. Thereaction mixture is then poured into icewater. The product is filteredand washed with water to give 4-n-pentylphenyl2-chloro-4-(4pentylbenzoyloxy)benzoate (3.1 g., 84%), m.p. 38-l22C. Theanalytical sample, m.p. 39-l22C is obtained by chromatography on Florisil and crystallization from ethanol. The theoretical valuescalculated for C d-1 C10 and the values actually found are as follows:

Anal. Calculated: C, 73.1; H, 6.7; Cl, 7.2. Found: C, 72.8; H, 7.0; Cl,6.9.

EXAMPLE 3 Compound No. 27 is prepared by stirring in pyridine a mixtureof (A) 2-chloro-4-(4-pentyloxybenzoyloxy)- benzoyl chloride and (B)p-cyanophenol. After stirring for 8 hours at room temperature, thereaction mixture is poured into ice-water and stirred for 30 minutes.The product is filtered off and purified chromatographically. Reactant(A) above is prepared by mixing ppentyloxybenzoyl chloride with2-chloro-4- hydroxybenzoic acid in pyridine. After heating this mixture,it is allowed to stand for 4 hours, whereupon the mixture is poured intoice-water and stirred. The product (Reactant A) is filtered off and anyremaining p-pentyloxybenzoic acid is removed by Soxhlet extraction.

The compounds of this invention are useful in electro-optical displaydevices. A typical cell used in forming electro-optical devices isanalogous to a parallel plate capacitor containing a liquid crystallinematerial as the dielectric. The plates are conductive and at least oneof the plates is transparent. When no potential is applied across thetwo plates or walls, the cell appears substantially transparent. Uponthe application of a d.c. or low frequency a.c. signal across theplates, the liquid crystalline material typically turns milky white.This white or cloudy condition is referred to as a scattering mode. Inmany scattering electro-optical cells, the cell becomes substantiallytransparent again when the voltage is removed.

The FlGURE illustrates an optical display device 9 comprised oftransparent cell walls 10 and 11 which are conductive, typically havinga conductive layer 12 and 13 of, for example, indium oxide on the innersurfaces thereof. The walls 10 and 11 are usually spaced apart adistance d typically in the range of about 2 to about 250 microns withbest results usually being obtained with a spacing of about 3 to about100 microns. Liquid crystalline material 17 is contained within cellwalls 10 and 11.

The layer of liquid crystalline material 17 is subjected to an electricfield of sufficient magnitude to alter or modulate the light scatteringproperties of the layer. The light scattering property of material 17 isnot affected until the electric field reaches a certain minimumthreshold value. This value depends, of course, on the particularmaterial or combination of materials being used, but is typically about10 volts per centimeter of layer thickness. In order to subject thelayer to an electric field, display device 9 includes a voltage source15 for applying a suitable electrical potential across conductive layers12 and 13. The potential applied can be direct voltage, including pulseddirect voltage, or low-frequency alternating voltage and typically has avalue between about 4 V. and about 80 V.

Device 9 can optionally have a reflective coating 14 when used in thereflective mode. Light source 16 can be positioned on either side ofdevice 9. Source 16 would be on the side of device 9 opposite theobserver when used in the transmissive mode. If used in the reflectivemode, source 16 is located on the same side as the observer andtypically is positioned so that the incident light is directed as shownby arrow A. In the zero or ground state, light which is not transmittedis reflected at an angle equal to the angle of incidence as shown byarrow B. When a voltage is applied, say, 15 V., the cell is placed inthe scattering mode and, therefore, the angle of reflected light nowchanges until it is essentially normal to the plane of cell 10 as shownby arrows C.

The cell configuration can be in the form of two spaced walls havingthereon conductive strips with the strips of one wall being arrangedorthogonal to those of the other wall to form an x-y grid. Each striphas a separate electrical connection to a voltage source. In thismanner, a crossconductor, addressable cell is formed which allows one toselectively apply the voltage necessary for dynamic scattering to anydesired portion of the grid. By the use of suitable logic, solid-stateelectronic systems can be utilized to address a large scale cell of thistype and display alphanumeric information.

Various addenda can be used in minor proportions with the presentcompounds and compositions. For example, when used in a dynamicscattering mode, it may be desirable to add various ionic species to theliquid crystalline material. Useful materials would include ionicsurface active agents having a long chain paraffinic substituent as wellas the ionic addenda described in Heilmeier et al U.S. Pat. No.3,499,112. Also aligning agents can be added if desired. Such agentsprovide homeotropic alignment of the liquid crystal molecules and somefind use in other than dynamic scattering cells. These agents arefurther described in copending Bucher U.S. application Ser. No. 218,243,filed Jan. l7, 1972, and entitled LIQUID CRYSTAL COMPOSI- TIONS (nowabandoned). Representative aligning agents are monomeric, nonionicsurface-active agents such as secondary or tertiary amines and ureashaving at least one paraffinic substituent. Such addenda as the latteramines and ureas, for example, would typically be added in a molar ratioof liquid crystalline compound to additive of about 1:10" to about 1210The following example demonstrates an embodiment of cells utilizing thepresent materials.

EXAMPLE 4 A cell is constructed of two Nesa coated glass electrodesseparated with a 1 mil. Teflon spacer. Compound No. 6 of Table I isplaced in the cell which is thermostatically controlled to maintainCompound No. 6 in its nematic phase. A potential of 35 volts AC isapplied across the cell. The application of this potential results inthe scattering of incident light Similar results are obtained with othermaterials described herein.

Dynamic scattering electro-optical cells are included as arepresentative embodiment of the present invention. The describedcompounds and compositions of this invention are also useful in othertypes of light modulating cells in addition to those involving a currentflow phenomena as in dynamic scattering. The present materials haveutility in so-called field effect cells as well. Other usefulelectro-optical cells or elements can contain a mixture of the presentnematic materials together with cholesteric molecules. Cells of thislatter type usually have information storage capability and aredescribed further by G. H. l-leilmeier in Liquid Crystal DisplayDevices, Sci. Amer., p. 100, April, 1970. In addition, the presentmaterials can be used in various acousto-optical and mechano-opticalcells as described, for example, in Dreyer U.S. Pat. No. 3,597,043,issued Aug. 3, 1971.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. in an electro-optical cell comprising means containing a film of atleast one liquid crystalline compound and means for applying an electricfield to said film, said field being of sufficient magnitude to alterthe light modulation properties of said film, the improvement whereinsaid compound is a substituted phenyl p-benzoyloxybenzoate having (a) amesomorphic temperature range of greater than about 50C. and/or (b) acrystal to mesophase transition temperature lower than about 100C, saidcompound having the formula:

0 ll ii R Q -C-QO-CQR: 8 7 Y R R R6 1: R 2

wherein:

one of R and R is an alkyl group or cyano group and the other is analkyl or alkoxy group; and at least one of R, R, R, R, R and R is acyano group or a halogen atom. 2. In an electro-optical cell inaccordance with claim 1 wherein in said formula:

one of R and R is an alkyl group having 1 to about 12 carbon atoms or acyano group and the other of R and R is an alkyl group having about 1 to12 carbon atoms or an alkoxy group having 1 to about 12 carbon atoms inthe alkyl moiety; and at least one of R, R, R, R, R, and R is a halogenatom and the remaining substituents are hydrogen atoms. 3. in anelectro-optical cell in accordance with claim 1 wherein in said formula:

one of R and R is an alkyl group or cyano group and the other is analkyl or alkoxy group; and at least one of R, R, R, R, R and R is acyano group and the remaining substituents are selected from a hydrogenatom, a methyl group, a nitro group or a halogen atom. 4. In anelectro-optical cell in accordance with claim 2 wherein in said formula:

R is an alkyl group having about 4 to 8 carbon atoms; R, is an alkylgroup having about 4 to 8 carbon atoms or an alkoxy group having about 4to 8 carbon atoms; and

only R is a halogen atom.

5. in an electro-optica] cell comprising means containing a film of aliquid crystalline material and means for applying an electric field tosaid film, said field being of sufficient magnitude to alter the lightmodulation properties of said film, the improvement wherein saidmaterial comprises a mixture of (a) about 35 to 65% by weight of a firstcompound having the formula:

O o "o R. 0-0 o-c R,

wherein:

R, is an alkyl group having about 4 to 8 carbon atoms;

R, is an alkyl group having about 4 to 8 carbon atoms or an alkoxy grouphaving about 4 to 8 carbon atoms; and

X is a halogen atom; and (b) about 65 to about 35% by weight of a secondcompound different from said first compound and having the above formulawherein R,, R, and X are as defined above.

6. The invention as described in claim 5 wherein said materialadditionally comprises up to about 30% by weight of at least onesubstituted phenyl benzoate of the formula:

0 I C v wherein;

one of R and R is an alkyl group or an alkoxy group and the other of Rand R is selected from an alkyl group, an alkoxy group and a cyanogroup.

7. In an electro-optical cell comprising means containing a film of aliquid crystalline material and means for applying an electric field tosaid film, said field being of sufficient magnitude to alter the lightmodulation properties of said film, the improvement wherein saidmaterial comprises a mixture of (a) about 5 to by weight of at least onesubstituted phenyl benzoate of the formula:

wherein:

one of R and R is an alkyl group or an alkoxy group and the other of Rand R" is selected from an alkyl group, an alkoxy group and a cyanogroup; with (b) about to 30% by weight of at least one liquidcrystalline compound as described in claim 1.

8. A liquid crystalline composition comprising about 35 to 65% by weightof 4-octylphenyl p-2-chloro-4-(4- heptylbenzoyloxy)benzoate and about 65to 35% by weight of 4-pentylphenyl 2-chloro-4-(4-pentylbenzoyloxy)benzoate.

UNITED sTATEs PATENT AND TRADEMARK OFFICE QERHMQATE GE QURREGTION PATENTN0. 3,915,883 DATED October 28, 1975 iNVENTOR S James P Van Meter andBruce H. Klanderman it is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 11, "elector-optical" should read electrooptical o Columni line #1, "the" should read with Column. i, that portion of thestructural formula of Table I reading 0 should read 0 a Column 6 line23, pheyl" should read phenyl Column 6, line 63, ipentylbenzoyloX shouldread i-pentylbenzoylox- Column 7 line 1, delete 'Anal".

Column 10 line 25, that portion of the structural formula reading 0should read gigncd and Sealed this A Nest:

RUTH C. MASON C. MARSHALL DANN (mnmissiunvr UfluI-I'lls' and TrademarksA Itesn'ng Officer

1. IN AN ELECTRO-OPTICAL CELL COMPRISING MEANS CONTAINING A FILM OF ATLEAST ONE LIQUID CRYSTALLINE COMPOUND AND MEANS FOR APPLYING AN ELECTRICFIELD TO SAID FILM, SAID FIELD BEING OF SUFFICIENT MAGNITUDE TO ALTERTHE LIGHT MODULATION PROPERTIES OF SAID FILM, THE IMPROVEMENT SAIDCOMPOUND IS A SUBSTITUTED PHENYL P-BENZOYLOXYBENZOATE HAVING (A) AMESOMORPHIC TEMPERATURE RANGE OF GREATER THAN ABOUT 50*C, AND/OR (B) ACRYSTAL TO MESOPHASE TRANSITION TEMPERAURE LOWER THAN ABOUT 100*C, SAIDCOMPOUND HAVING THE FORMULA:
 2. In an electro-optical cell in accordancewith claim 1 wherein in said formula: one of R1 and R2 is an alkyl grouphaving 1 to about 12 carbon atoms or a cyano group and the other of R1and R2 is an alkyl group having about 1 to 12 carbon atoms or an alkoxygroup having 1 to about 12 carbon atoms in the alkyl moiety; and atleast one of R3, R4, R5, R6, R7, and R8 is a halogen atom and theremaining substituents are hydrogen atoms.
 3. In an electro-optical cellin accordance with claim 1 wherein in said formula: one of R1 and R2 isan alkyl group or cyano group and the other is an alkyl or alkoxy group;and at least one of R3, R4, R5, R6, R7 and R8 is a cyano group and theremaining substituents are selected from a hydrogen atom, a methylgroup, a nitro group or a halogen atom.
 4. In an electro-optical cell inaccordance with claim 2 wherein in said formula: R1 is an alkyl grouphaving about 4 to 8 carbon atoms; R2 is an alkyl group having abOut 4 to8 carbon atoms or an alkoxy group having about 4 to 8 carbon atoms; andonly R5 is a halogen atom.
 5. In an electro-optical cell comprisingmeans containing a film of a liquid crystalline material and means forapplying an electric field to said film, said field being of sufficientmagnitude to alter the light modulation properties of said film, theimprovement wherein said material comprises a mixture of (a) about 35 to65% by weight of a first compound having the formula:
 6. The inventionas described in claim 5 wherein said material additionally comprises upto about 30% by weight of at least one substituted phenyl benzoate ofthe formula:
 7. In an electro-optical cell comprising means containing afilm of a liquid crystalline material and means for applying an electricfield to said film, said field being of sufficient magnitude to alterthe light modulation properties of said film, the improvement whereinsaid material comprises a mixture of (a) about 5 to 70% by weight of atleast one substituted phenyl benzoate of the formula:
 8. A liquidcrystalline composition comprising about 35 to 65% by weight of4-octylphenyl p-2-chloro-4-(4-heptylbenzoyloxy)benzoate and about 65 to35% by weight of 4-pentylphenyl 2-chloro-4-(4-pentylbenzoyloxy)benzoate.